Thread gauge



THREAD GAUGE Maynard E. Kraushaar, Pasadena, Calif. Application May 18,1953, Serial No. 355,783 2 Claims. (Cl. 33199) This invention relates toa thread gauge, and more particularly to a gauge for use by a machinistwhile engaged in the process of forming a screw thread.

Conventional thread gauges, for example of the ring or thread wire type,are subject to a number of disadvantages in that they are difficult touse and do not indicate te the machinist what must be done to correct aninaccuracy in the thread being formed. In addition, conventional gaugesdo not show up variations in the angles of the thread faces relative tothe axis of the screw, or variations in the dimensions of variousportions of the thread. A ring gauge, for example, merely indicates tothe machinist that a previously formed thread is substantiaily correct,and does not enable the machinist to determine the exact manner in whichan improperly formed thread may be corrected. A thread wire gauge issubject to the ie defects since it also does not-indicate how much mustbe taken off on the next cutting or grinding operation in order toreduce the thread to the desired size. Furthermore, ring and thread wiregauges may not conveniently be used at various points along a screwthread to indicate when one portion of the screw is at variance withanother, and do not indicate when one or more faces of the thread arenot at an exact sixty-degree angle with the axis of the screw.

In view of the above problems characterizing the field of thread gauges,it is an object of the present invention to provide a simple,inexpensive, and reliable thread gauge which may be easily employed tocheck various portions of a screw thread, and when so employed willindicate to the operator how much metal to take off on the Aext cuttinfror grinding operation to provide a thread having the desired dimensions.

Another object of the invention is Vto provide a thread gauge adapted toindicate the precise pitch diameter of a standard screw thread, and alsowhen any of the lfaces of a standard screw thread is not at a precisesixty-degree angle with the longitudinal axis of the screw being formed.

An additional object is to provide a handle which may he readilymanipulated to position the gauge at various points on the thread, yetwhich will not interfere with the precise operation of the body of thegauge.

These and other objects and advantages of Vthe invention will be morefully set forth in the following specification and claims considered inconnection with the `atthed drawing to which they relate.

in the drawing:

Figure l is a greatly enlarged longitudinal elevational viewillustrating the thread gauge in mounted position on a lead screw;

Figure 2 is a perspective view showing a micrometer as employed inreading the .resultant distance across the screw and gauge; and

T`igure 3 is a central sectional view, longitudinally of the gauge,illustrating the construction and mounting of the handle elements.

Referring to the drawing, the gauge, indicated gentates Patent()2,731,730 Patented Jan. 24, 1956 'ice erally by the reference character10, is illustrated as employed in forming a precision lead screw 11 ofthe standard type. The screw thread being standard in the presentillustration, it will have straight or iiat sides 12 and '13 which forma sixty-degree angle with Yeach other as well as with the longitudinalaxis of the screw. Although `the lead screw 11 is illustrated `as havinga at 14 at its root and a corresponding VHat .15 at its ridge, the gaugeof the present invention will work equally well where the thread sides12 and 13 come to a sharp corner Vat either or both the root and theridge.

The gauge 10 comprises a and a handle structure which Y tion 18 and aexible portion 19. As will be described in detail subsequently, thehandle structure is constructed so that the machinist may manipulate thegauge with ease and without interfering with the accuracy of fthegauging operation.

Block 17 is precision formed of hardened tool steel, and is anequilateral triangle in transverse section so that a sixty-degree angleis formed between intersecting faces. Any two faces of block 17 willtherefore rest, as shown in Figure 1, in exact abutment with the opposedthread sides 12 and 13 when the block is mounted transversely of 'thescrew axis as indicated.

it is essential, for accurate use of the gauge, `that a maximum bearingsurface or area result when the gauge is positioned on the lead screw.Accordingly, the three corners or edges 21-23 of the block are formed'with flats of different widths so that the inner corner of 'the blockmay be selected for positioning as close as possible to the thread root14 without actually engaging it. vOne such flat, at the corner 21, isapproximately .002 inchin width, while the flats at the corners 22 and23 are .008 and .015 inch in width, respectively. It is to be understoodthat the showing in the drawing is greatly 'exaggerated both as to thewidths of the ats and as to the actual size of the block 17. In apreferred construction, the length of the block 17, transversely of thelead screw 11, is approximately half an inch.

In using 'the body portion 17 of thread gauge 10, the machinist selectsa piece of cylindrical stock of given major diameter, indicated at D inFigure l, and uses a lathe or thread grinder `to rough 'form the thread.y'Such rough formingis effected by standard methods and with knowledgeof the root diameter R, the pitch diameter E, 'and the pitch. After theleadscrew is thus rough formed, gauge block 17 is positioned with two ofits faces in abutment, respectively, with the thread sides 12 vand 13.The inner Yedge 21, 22, or 23 is selected as the =one whichwill beclosest to the root 14 as previously mentioned. A micrometer, indicatedin Figure 2 at 26, is 'then employed to take the reading M across bothblock 17 and 'the screw 11.

It can be shown that the inches, equals triangular b'ody block 17, isformed with a rigid pormicrometer reading M, in

for the national standard screw thread, where D `is vthe major diameter,in inches, G is the length, in inches, of an altitude of the equilateraltriangle making up'the block 17, and N is the pitch in threads per inch.The correct reading of M for any thread may therefore be determinedsince D and N are known in any shop problem, and G is known for 'anygauge. The following is an extract from a table which may be utilized inthe shop to save the machinist from vcalculating Vwhat the reading of Mshould be for various standard threads and standard major diameters:

After the rough forming operation, the actual reading of M is comparedto the value given either by the above table or by calculation, andfinish cuts are taken until the reading of M on micrometer 26 is thesame as the table reading, it then being known that the thread isperfectly formed and has the desired pitch diameter.

. To illustrate the above, a representative problem will be described.Let it be assumed that it is desired to form an -80 national standardthread on stock having a basic major diameter of .060 inch. Referring tothe above table, the machinist will note that the reading of M for sucha thread will be .42553 inch. By standard shop processes the machinistwill form a rough thread which is somewhat larger than the nishedproduct. He will then position the block as described above, and take areading with micrometer 26. Such a reading would, for example, be .42560inch, which is a little less than .0001 greater than the correctreading. Using this information, the machinist will be able to set histools with exact knowledge of how much to take oft on the next or finishcut. Another reading is taken after the finish cut is made, and it isknown that the thread is perfectly formed if the micrometer reading andthe value of M on the table coincide. The process is, of course,repeated if the micrometer reading is again slightly larger than thetable value of M.

It is a feature of the invention that the reading of M is not merelytaken at one location, but instead is taken at a number of points alongthe full length of screw 11. In this way it is determined whether thevarious sections of the screw are exactly equal to each other, as wellas whether the sections each have the correct value of M for the threadwhich it is desired to form. When the readings of M are thus taken atone or more points along the screw, it may be readily determined whetheror not the faces 12 and 13 form exact sixty-degree angles with eachother as well as with the longitudinal screw axis. This is to bedistinguished from conventional gauges, which may be utilized todetermine whether the thread sides form a sixty-degree angle with eachother, but which do not indicate when one or the other of the threadsides is tilted with respect to the screw axis. Thus, for example, theside 12 may form a sixty-degree angle with side 13, yet it may form anacute angle of sixty-two degrees with the longitudinal axis of the screwif the side 13 forms an acute angle of fifty-eight degrees. Suchundesired tilting of the thread sides is readily determined, accordingto the present invention, by merely sighting between the micrometer endface 27 and the abutting surface of gauge block 17. If any light appearsbetween these components, the machinist will know that the block 17, andconsequently the thread sides 12 and 13, are titled with respect to thescrew axis.

In view of the above, it may be seen that the percise positioning ofblock 17 is of extreme importance since the gauge will not read properlyif the block faces are not in continuous engagement with the threadsides 12 and 13. Where the abutment between the faces of block 17 andthe thread sides is not perfect, the reading will be incorrect and thestep of sighting between the micrometer end 27 and the cooperating blockface will not give a true indication of whether the thread sides aretilted with respect to the screw axis.

According to the present invention, the precise mounting of block 17 isaccomplished when the slight micrometer pressure is applied, even thoughthe initial block mounting may be improper and even though the lingersof the machinist are not steady. Such desired action results from use ofthe handle component of the gauge, which consists of a rigid portion 1Sand flexible portion 19 as previously indicated. The rigid portion 18takes the shape of a bail, of circular section, having side portions 29extending parallel to each other and in planes perpendicular to thelongitudinal axis of gauge block 17 The sides 29 are connected, remotefrom block 17, by an integral end section, indicated at 31, extendingparallel to the bloclr axis. The portions of bail sides 29 adjacentblock 17 are bent inwardly at right angles for loose insertion into anaxial passage 32 bored in the block. The clearance 33 between each hailend and the block 17 is sufficient to permit substantial movement of therigid portion 18 of the handle without any interference with the precisemounting of gauge block 17.

rlhe flexible component 19 of the gauge handle structure takes the formof a strip of very thin aluminum, one end 34 of which is bent around thebail portion 31 and secured, as by gluing, to the main body of thestrip. The flexible component 19 may, if desired, be inscribed with theabove stated equation so that it will be readily available to themachinist as he uses the gauge.

In the operation of the handle structure as employed in connection withthe block component of the gauge, the machinist grasps the rigid portion18 of the handle and carries the block 17 until it is in approximateposition. The micrometer 26 is then placed around the screw and blockand the iiexible component 19 of the handle is grasped, for examplebetween two lingers of the machinist, to maintain the rigid component 18ont of engagement with lead screw 11 or other interfering structures.While the component 19 is thus held, the micrometer 26 is turned toobtain the reading.

When the gauge 10 is employed in this manner, the block 17 is nestedbetween the thread sides 12 and 13 by pressure due almost entirely toits Weight and to the slight force exerted by the micrometer 26. Therigid or bail portion 18 of the handle in no way alects the iinalpositioning of the block 17 since this portion is not grasped by themachinist during the final portions of the operation, and furtherbecause the clearances 33 are adequate to permit slight shifting of thebail 18 without any effect on the block. The liexible component 19 ofthe handle, although grasped during the final reading operation, doesnot affect the iinal positioning of block 17 since any vibration orunsteadiness of the machinists fingers will be damped before reachingthe bail. If not completely eliminated, such a vibration will have noeffect on the block 17 because of the clearance 33 between the bail andblock. The invention thus provides for the ready manipulation andpositioning of the gauge block 17 by a handle which is speciallydesigned to prevent any interference with the accuracy of the reading.

The described operation of the handle components in facilitating thepositioning of block 17 in the absence of interference with the accuracyof a reading, is further enhanced since the handle components 18 and 19are extremely light and will not have substantial effect in tilting theblock 17 even though the flexible strip 19 is accidentally releasedduring the taking of a reading. Since the block 17 will not be tilted,the accuracy of the reading of M, as well as the accuracy of a sightbetween micrometer end 27 and the cooperating face of the gauge, will beleft substantially unimpaired.

While the particular apparatus herein shown and described in detail isfully capable of attaining the objects and providing the advantageshereinbefore stated, it is to be understood that it is merelyillustrative of the presently preferred embodiments of the invention andthat no limitations are intended to the details of construction ordesign herein shown other than as dened inthe appended claims.

I claim:

l. A thread gauge, comprising a small metal block any transverse sectionof which is an equilateral triangle, said block having an axial boreformed therethrough and of substantial diameter, a light-weight rigidmetal bail ha"- ing parallel sides extending transverse to the axis ofsaid block and connected at their ends remote from said block by anintegral end portion formed parallel to said axis, the ends of said bailsides adjacent said block being inwardly bent at right angles to saidsides and extending loosely into opposite ends of said bore, and a thinstrip of highly exible material mounted on said end portion of saidbail,

6 said thin strip being adapted to be held by an operator during the nalportions of a gauging operation.

2. The invention as claimed in claim 1, wherein said flexible materialis aluminum, and substantial clearance is provided between said ends ofsaid bail sides and the Wall of said bore, whereby vibration of saidstrip during a gauging operation is ineffective to alter the position ofsaid block. Y

References Cited in the file of this patent UNITED STATES PATENTSSimmons Apr. 5, 1949 Russell et al Nov. 14, 1950 OTHER REFERENCESPublication- Popular Mechanics, September 1945, page 138. (Copy inLibr.)

